In pressurized water reactors for the nuclear production of power, a pressurized fluid is passed through the reactor core and, after being heated in the core, is passed through heat transfer tubes that are positioned in a secondary side of a steam generator. In the secondary side of the steam generator, the heat transfer tubes transfer heat to a secondary fluid to produce steam that is then used to operate a turbine for production of electrical power.
The provision of emergency feedwater systems for the secondary side of the steam generators of a pressurized water reactor is made in order to supply feedwater to the steam generators following an accident or transient conditions when the main feedwater system is not available, thereby maintaining the capability of the steam generators to remove plant stored heat and reactor core decay heat by converting the emergency feedwater to steam which may then either be discharged to the condensor or to the atmosphere.
Such emergency feedwater systems generally comprise a source of emergency feedwater, such as a supply of water contained in a storage tank, and associated lines, pumps and valving systems to direct the emergency feedwater, when necessary, to the steam condensors. In order to assure operation of the system under various adverse conditions, means must be provided to effect operation of the emergency feedwater system for example in the event of loss of electrical power, or in the event of a passive failure such as a pipe rupture or an active failure such as a failure of a valve to respond to a signal to open or close. In addition, provision should be made to address even remote possibilities of interruption of an emergency feedwater system, such as fires or other external events, such as air craft impacts, explosions, or the like, which might impair the operability of the system.